Geology of Southern India. 197 



ginal state of igneous fluidity to that in which they now 

 exist, may safely be concluded, from the experimental truth, 

 that variation of temperature is one of the most fruitful 

 sources of this agent ; and should it ever be satisfactorily 

 shewn that a subjection to electric agency confers on the 

 particles of matter that peculiar polarity, which disposes 

 them to group themselves in determinate figures, and under 

 determinate laws, no element will be wanting for the appli- 

 cation of such a principle of explanation to the present case. 



The plain of the Carnatic is diversified by the occasional 

 occurrence of connected, as well as detached hills. A peculiar 

 feature is to be remarked in several of those in the immediate 

 vicinity of Vellore. Individual hills are observed to rise 

 abruptly from the plain, like islands in the midst of an 

 ocean of sand, of the most perfectly conical shape, and want- 

 ing only the crater, with its accompanying cloud of smoke, 

 to complete their resemblance to existing volcanos. These 

 hills are usually at some distance from the connected ranges, 

 and as an explanation of the peculiarity, it might be con- 

 ceived that the upraising force had in the one case acted 

 on a line to produce the range, while to produce these in- 

 sulated and conical hills it had been concentrated in a focus 

 or point. 



At Palleconda, a small town about 14 miles south-west 

 of Vellore, I crossed a tract of country which has been 

 described by Dr. Benza, an observer who has added con- 

 siderably to our knowledge of the geology of Southern 

 India. The plain on which the town stands is sandy, and 

 strewed over it there are many weathered masses of 

 sienite, which natural sections afforded by the deep nullah 

 beds prove to be the underlying rock of the whole. Tra- 

 versing this there are as usual dykes of trap and por- 

 phyry. The latter is of a peculiar kind, the porphyritic 

 crystals being of felspar imbedded in a matrix of quartz. 



